The present invention is related to apparatus for elevationally moving an agricultural implement between a ground engaging operative position and an above ground transport position.
Since variable stroke cylinder assemblies are both complicated and expensive, elevational adjustments in agricultural machinery have been typically achieved by mechanical devices external to the cylinder assemblies. However, where multiple cylinders are used side-by-side across the machinery, normal fluid leakage will result in the cylinder assemblies becoming out of phase with one another. Rephasing cylinders are available, but are corrective only at one or both ends of a cylinder stroke. It is therefore desirable to design a cylinder assembly adjustment that varies the working depth of an implement, but accommodates full extension and retraction for frequent rephasing purposes. A secondary result achieved herein is the maintenance of a constant travel position of the implement for all working depth adjustments.
One prior solution has been use of fixed stroke hydraulic cylinders with threadably adjustable extensions. The threaded extensions can be turned to extend or shorten the piston shaft of the cylinder and thereby locate the movable tool frame about its pivot axis. The threaded extensions work well to achieve a variable working depth of the tool, but the resulting transport position varies directly with the different working depth settings.
Another solution has been use of solid blocks that encircle the extended piston shaft and limit its available amount of contraction. This in turn limits rephasing of the cylinders to those times when the cylinders are fully extended.
U.S. Pat. No. 2,979,140 to McKenzie shows a moldboard plow frame construction wherein elevationally spaced abutments restrict the stroke of a wheel-tool frame connecting cylinder. The working depth of the tool can be varied, but the stroke limits are confined with the spacing of the abutments.
U.S. Pat. No. 2,320,742 to C. E. Newkirk shows a cylinder arrangement innerconnecting a pivoted wheel frame and a tool frame. The piston shaft includes a turnbuckle arrangement for setting the operating depth and transport height of the tool. The operating depth setting automatically determines the transport height.
U.S. Pat. No. 3,153,988 to H. E. Warspler discloses a pneumatic piston actuator with stroke adjustment features provided on the cylinder body. The stroke is variable at its extension but fixed upon retraction. A turnbuckle arrangement is provided on the piston shaft to selectively vary the shaft length. The stroke adjusting abutments on the cylinder body confine the piston to a stroke that is usually substantially less than its full length.
A problem presented by a fixed stroked cylinder being used for raising and lowering a ground working implement is well illustrated by U.S. Pat. No. 3,912,018 to J. F. Brundage et al. The Brundage mechanism includes a complex leveling system for holding a ground working tool level when hoisted to a transport position. If the level mechanism were not present, the implement would tilt awkwardly behind the towing vehicle upon actuation of the lift cylinder assembly to move the tool from its lowered working elevation.
The Chandler et al U.S. Pat. No. 2,830,519, illustrates in FIGS. 2 and 14 a stroke limiting device for selectively adjusting operating depth and transport height of a ground working tool. A threaded shaft on a pivoted frame member includes nuts on opposite sides of a fixed abutment. The nuts will engage and limit motion of the pivoted frame member at selected positions of the tool support. The nuts and abutments limit the otherwise full stroke of the cylinder.
Limitations placed on the stroke length as illustrated by the above referenced patents, inhibit "rephasing" of cylinders used in a hydraulic series across a large implement, since "rephasing" or synchronizing of the cylinders is normally accomplished only at full extension or retraction of the cylinders.
The present invention provides variable adjustment of operating depth for a ground working tool while maintaining a consistent transport height and utilizing the full cylinder stroke in both directions. This allows rephasing cylinders to be synchronized across the implement at each cylinder stroke. Adjustment of the operating depth has no affect on transport height, assuring that the ground working implement will be carried at a preselected height each time it is raised from the ground.